We collected several native and derivative data sets of NB1 (space group P2 1212). Attempts to solve the structure by molecular replacement using whole calmodulin as well as the domains individually as a model have been continued but have so far not yielded a consistent solution. Internal flexibility of the elongated calmodulin molecule has prevented molecular replacement in numerous other cases in which researchers had to resort to heavy atom multiple isomorphous replacement (MIR) methods. Heavy atom derivatives (Patterson maps of Harker sections) have not resulted in interpretable Patterson peaks.